How to rotate, crop, and straighten pictures in Photos for OS X

When you don't have time to carefully line up and perfectly frame every photo, you just need to shoot first and fix it in post later.
That's where straightening and cropping come in. Whether the horizon or a building looks oddly angled, or extra people or space are stealing focus from your subjects, Photos for OS X has just exactly those tools to help you line up what you want and cut out what you don't, so that even if you didn't frame the perfect photo, you can still end up with it. Also, if you need to rotate or flip a picture, you can do that too!